In semiconductor manufacturing, double patterning (DP) is a process for forming aluminum lines which is difficult for application in a dual damascene process. In one method of forming a double pattern, a first photolithography process is performed using a hard mask. A first etching process is then performed on the hard mask and then the hard mask is patterned by a second photolithography process. An underlying metal layer formed under the hard mask is then etched to form metal lines. Another double patterning method involves etching the underlying metal layer using a photoresist instead of a hard mask. After stripping the photoresist, a second photolithography process for etching the metal layer is performed to form final metal lines. In still another double patterning method, first and second exposure processes are performed before performing a developing process to thereby form final metal lines. As previously noted, such double patterning methods are disadvantageous since they are difficult to apply in a dual damascene process.